The discovery of the Lulo Rose, a pure pink diamond, in Angola is thought to be the largest such gemstone found in 300 years - and interest is already intense ahead of its sale.

The ancient gem was found in Angola at the Australian-run Lulo alluvial diamond mine, which focuses on scouring river beds, and so how important is this discovery? Well, just one in 10,000 diamonds is coloured pink, so finding one is very special indeed.

This monster is a type 2a diamond, which means it has few or no impurities.

The Lucapa Diamond Company hasn’t given a value for the uncut gem yet, but another such rock, called the Pink Star and weighing 132 carats, sold for over £58 million at a Hong Kong auction in 2017.

One carat equals 0.2 of a gram.

The Angolan mine is opencast, which means miners sift through thousands of tonnes of alluvial riverbed gravel from the Cacuilo River, hunting for rough diamonds that have collected in deposits over millions of years after eruptions forced them to the surface.

The world’s largest known pink diamond is the Daria-i-Noor, discovered in India in the 1700s, weighing in at 182 carats.

The largest clear diamond is the 3,100-carat Cullinan I found in South Africa in 1905, which is part of the Crown Jewels.

To discuss the importance of this historic find and what else lies beneath the Earth’s crust, The Leader’s joined by Robin Hansen, curator of minerals and gemstones at London’s Natural History Museum.

We also discuss the cutting process and how to check a gem’s provenance if you’re shopping for that special gift.

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